122 BIOLOGY OF THE PROTOZOA 



structures. According to Zuelzer the pseudopodia of Wagnerella 

 borealis are withdrawn at times, owing to the contraction of the 

 entire complex of radiating fibrils, and basal bodies lying at the 

 bases of the axopodia become grouped in a zone of granules about 

 the central grain. When the pseudopodia are again formed the 

 granules migrate centrifugally to the periphery and, as basal bodies, 

 give rise to the axial filaments. 



In Heliozoa without a central granule the axial filaments in some 

 cases center in the nucleus in which there are many distinct and 

 definite granules of uniform size distributed about the outer zone, 

 from each of which an axial filament appears to rise (Fig. 66). 

 In Camptonema nutans the nuclei are multiple and, according to 

 Schaudinn, each one gives rise to a single pseudopodial element, 

 but in Actinosphaerium eichhornii, which is also multinucleate, the 

 axial filaments apparently have no connection with either nuclei or 

 central kinetic elements. 



Apart from kinetic elements like centroblepharoplasts which, at 

 the same time, are centers of mitotic activity of the nucleus and of 

 kinetic activity of the motile organs, there are comparatively few 

 examples of kinetic elements comparable with centrosomes of Meta- 

 zoa. These are best represented in non-motile organisms such as 

 Sporozoa, whereas in freely-moving types there is always some pecu- 

 liar feature which makes the homology with centrosomes doubtful. 



A frequently cited example of a centrosome in Protozoa was first 

 described by Hertwig in the case of Actinosphaerium eichhornii 

 (Fig. 6<S). Here, during the formation of the first maturation 

 spindle minute granules of chromatoid substance are cast out 

 of the nucleus and condensed into one or two minute centrioles from 

 which fibrillar structures radiate into the cytoplasm and throughout 

 the nucleus. This structure, however, has no permanent relation 

 to the cytoplasm or nucleus, but disappears after the first maturation 

 spindle is formed while subsequent maturation spindles and spindles 

 of division stages are characterized by pole plate formation (see 

 p. 65). Much more typical centrosomes are found by Arndt (1924) 

 in Hartmannella klitzkei (Fig. 58, p. 106) and in the Gregarinida, 

 especially in the Monocystis types, where they have been described 

 by Leger, Brasil, Mulsow, Doflein, and others. In Monocystis 

 rostrata, for example, a single centrosome with marked astral radi- 

 ations lies outside the nuclear membrane (Fig. 55, p. 101). An am- 

 phiaster is formed as in egg cells of Metazoa, and a complete mitotic 

 figure results. Similar centrosomes occur in Urospora lagidis, St., 

 Gonospora varia, Leger, and Stylorhynchus longicollis, St. 



In general we do not find the same types of kinetic elements in 

 Infusoria that are found in other forms of Protozoa. Blepharo- 

 plasts, parabasal bodies and centrosomes are still unknown in 

 filiates, although certain peculiar kinetic elements are present here 



